242 ELEMENTS OP BOTANY. 



(c) The coiled spore-cases or sporangia, lying partly covered by the 

 indusium. How do these sporangia discharge their spores ? 



Make a drawing, or several drawings, to bring out all these points. 



Examine some of the sporangia, dry, with a power of about 50 or 75 

 diameters, and sketch. Scrape off a few sporangia, thus disengaging 

 some spores, mount the latter in water, examine with a power of about 

 200 diameters, and draw. 



302. Life History of the Fern. — When a fern-spore is sown on 

 damp earth it gradually develops into a minute, flattish object, called a 

 prothaUium, Fig. 208. It is a rather tedious process to grow prothallia 

 from spores, and the easiest way to get them for study is to look for them 

 on the earth or on the damp outer surface of the flower-pots in which 

 ferns are growing in a greenhouse. All stages of germination may 

 readily be found in such localities. 



Any prothallia thus obtained for study may be freed from particles of 

 earth by being washed, while held in very small forceps, in a gentle 

 stream of water from a wash-bottle. The student should then mount 

 the prothallium, bottom up, in water in a shallow cell, cover with a large 

 cover-glass, and examine with the lowest power of the microscope. Note : 



(a) The abundant root-hairs, springing from the lower surface of the 

 prothallium. 



(6) The variable thickness of the prothallium, near the edge consisting 

 of only one layer of cells. 



(c) (In some mature specimens) the young fern growing from the 

 prothallium, as shown in Fig. 208, B. 



The student can hardly make out for himseH, without much expendi- 

 ture of time, the structure of the antheridia and the archegonia, by the 

 co6peration of which fertilization .takes place on much the same plan as 

 that already described in the case of mosses. The fertilized oosphere of 

 the archegonium gives rise to the young fern, which grows at first at the 

 expense of the parent prothallium but soon develops roots of its own and 

 leads an independent existence. 



The mature fern makes its living, as flowering plants do, by absorption 

 of nutritive matter from the soil and from the air, and its abundant 

 chlorophyll makes it easy for the plant to decompose the supplies of 

 carbonic acid gas which it takes in through its stomata. 



generally accessible form, but has no indusium. Pteris aquilina is of world-wide 

 distribution, but differs in babit from most of our ferns. The teacher who wishes to 

 go into detail in regard to the gross anatomy or the histology of ferns as exemplified 

 in Pteris will And a careful study of it in Huxley and Martin's Biology, or a fully 

 illustrated account in Sedgwick and Wilson's Biology. 



